Single-file databases -- how do they do it?

Hello,
How do single-file databases do it? If a database has, say, 10 tables,
does that mean that the single-file is just a trick to hold ten
separate 'boxes' inside, one for each table, or someone has found a
way to store all the tables of a database in one big single table? Can
someone un-curious-ify me?
Thanks,
gk